Synthesis Gas and its Derivatives (Part - 2) | Chemical Technology - Chemical Engineering PDF Download

Formaldehyde 

Some major intermediates derived from formaldehyde are chelating agents, acetal resins, 1,4-butanediol, polyols, methylene diisocynate. It is also used for the manufacture of wide variety of chemicals, including sealant, herbicides, fertilisers, coating, and pharmaceutical. Product profile of formaldehyde is given in Table M-VII 4.7.  

Formaldehyde is commercially available as aqueous solution with concentration ranging from 30-56 wt.% HCHO. It is also sold in solid form as paraformaldehyde or trioxane. The production of formaldehyde in India has been growing at a fairly constant rate during last ten years. There are presently about 17 units in India. Installed capacity and production of formaldehyde during 2003-04 was 2.72 lakh tonnes and 1.89 lakh tonnes respectively. 

Various industrial processes for manufacture of formaldehyde using silver and ironmolybdenum catalyst are given below: 

Catalyst                                                      Process licensor

Silver catalyst processes                           Bayer, Chemical construction, Ciba, DuPont, IG Farben, CdF Chemie process, BASF process, ICI process,  

Iron-molybdenum catalyst processes        Degussa process, Formox process, Fischer-Adler, Hiag-Lurgi, IFP-CdF Chimle Lumus, Motedisous, Nikka Topsoe, Prolex 

Process diagram for manufacture of formaldehyde using silver and iron-molybdenum catalyst is shown in Figure M-VII 4.5 and Figure M-VII 4.6 respectively. 

Table M-VII 4.7: Product Profile of Formaldehyde 

Table M-VII 4.8: World Acetic Acid Capacity and Consumption Pattern 

 Table M-VII 4.9: Installed Capacities of Acetic Acid in India 

Table M-VII 4.10:Market Share of Major Acetic Acid Manufacturer

 Table M-VII 4.11: Product Profile of Acetic Acid  

Chloromethanes (Methyl Chloride, Methylene Dichloride, Chloroform, Carbon Tetrachloride) 

Chlorinated methanes, which include methyl chloride, methylene dichloride, chloroform and carbon tetrachloride, are important derivatives of methane and find wide application as solvents and as intermediate products. Product profile of Chloromethane is given in Table M-VII 4.12

Table M-VII 4.12: Product Profile of Chloromethane 

Process Technology

There are two major routes for the manufacture of chloromethane:

• Direct chlorination of methane
• Through methanol route

 Direct Chlorination of Methane: Chlorination of methane (natural gas) is carried out at around 400-450 oC during which following reaction takes place: 

Dimethyl Formamide [Hcon(Ch₃)₂]

Dimethyl formamide is one of widely used solvents in the manufacture of acrylic fiber. Because of its high dielectric constant, aprotic nature, wide liquid range and low volatility, dissolving power it is frequently used for as solvent.  

Process Technology

Dimethyl formamide is made by following two processes:

Two step process

Process involves carbonisation of methanol to methyl formate using basic catalyst and reaction of methyl formate with dimethylamine.

Acetylene

It plays important role during and after World War II in providing feedstock for large number of organic chemicals when petrochemical industry was not well developed. Acetylene’s highly reactive triple bond provided a ready “handle” for chemists to grab onto for designing process chemistry Safety issues involved with handling of large volumes of acetylene and its expense are big problem with adoption of acetylene based processes. The process of acetylene requires much energy and is very expensive. of attractive petrochemical feedstock. Acetylene is still being used for manufacture of chemicals.  

Various Routes for Acetylene:

Calcium Carbide Route: This is the oldest method for production of acetylene and still acetylene is produced by this process in small scale as well large scale. Calcium carbide is produced by reacting lime with coke at temperature 2,000-2,100 ^oCin an electric furnace. Two processes produce acetylene from calcium carbide process: Wet process and Dry process. Dry process is preferred as in case of calcium hydroxide, which is produced during the process (is produced in the form of dry calcium hydrate).

CaC₂ +2 H₂O→ C₂H₂ + Ca(OH)₂ 

Acetylene from Cracking of Hydrocarbons: Cracking of hydrocarbons such as methane, ethane, propane, butane, ethylene, and natural gas can make acetylene.

• 2 CH₄ → C₂H₂ +3 H₂ 
• C₂H₄ →C₂H₂+H₂ 
• C₄H₁₀ →C₂H₂+C₂H₄+2 H₂

Product Derived from Acetylene: Acetylene is extremely reactive hydrocarbon and was initially was used for the manufacture of  large number of  chemicals which are now being derived from acetylene route. Product profile of acetylene is given  in Figure M-VII 4.7 and Figure M-VII 4.8

Figure M-VII 4.7: Product Profile of Acetylene

Acetaldehyde:

Acrylonitrile: HC≡CH+HCN    →           HC=CH= CH2=CHCN 

Chlorinated solvents: 

Vinyl acetate:

HC≡CH+CH₃COOH  →      CH₂ = CHOOCCH₃ 

Chloreprene 

HC≡CH+CH₃COOH         CH₂ = CHOOCCH₃

CH₂ = CHOOCCH₃+Cl₂   CH₂=CClCH=CH₂

Vinyl Chloride and Vinylidene Chloride   

HC≡CH+HCl  →         CH₂ =CHCl 

CH₂ =CHCl+Cl₂  → CH₂ ClCHCl₂

CH₂ ClCHCl₂ →  CH₂ = CCl₂+ HCl

Vinyl fluoride: 

HC≡CH+ HF   → CH2=CHF

Figure M-VII 4.8: Reactions in Acetylene derived Chemicals